Method of making a magnetic core



Oct. 22, 1963 B. B. ELLIS METHOD OF MAKING A MAGNETIC CORE 2Sheets-Sheet 1 Original Filed Dec. 11. 1957 INVENTOR WITNESSES:

Belvin B. Ellis BY;

ATTORNEY Miww Oct. 22, 1963 B. B. ELLIS 3,107,415

METHOD OF MAKING A MAGNETIC CORE Original Filed Dec. 11. 1957 2Sheets-Sheet 2 F|g.7. 5 o 84 84 5Q 74 64 74 F|g.l0.

Fig. 8.

ted States 6 Claims. or. 29-l55.58)

This invention relates to wound type magnetic cores and moreparticularly to improvements in such cores, and the method of making thecores.

This application is a division of my application Serial No. 702,096,filed December 11, 1957, and assigned to the same assignee as thisapplication.

In the making of a core and coil assembly for inductive apparatus, twoor more wound type cores, each effectively out only once through thelaminations, are sometimes fitted through the window of a preformedWinding or coil. In order to allow the outer laminations of each core tobe conveniently fitted through the window of the preformed winding, itis necessary that a predetermined amount of space he left between thecores fitted through the window. The latter arrangement reduces theamount of space that can "be utilized within the window of the preformedwinding or coil. In addition, if only a small space is left between thecores fitted into the window of the preformed winding, it is found thatthe outer laminations of each core may be deformed in order to fit theouter laminations of each core through the window of the preformedwinding. Any deformation of the outer laminations results in at least asmall increase in the losses of a wound type core. Fitting the outerlaminations of each core through the window of the preformed windingalso presents difliculties in the making of core and coil assembliessince the fitting may have to bedone manually which requires additionaltime and care in the manufacture of a core and coil assembly. It is,therefore, desirable to provide a wound type core which can be conveniently fitted through the window of a preformed winding and yet morefully utilize the space in the window of a preformed winding to obtain amaximum space factor in the core and coil assembly and thereby alsoreduce the conductor requirements in the preformed coil.

it is, therefore, an object of this invention to provide a new andimproved wound type core for inductive apparatus.

Another object of this invention is to provide a new and improved methodof making a wound type magnetic core.

A further object of this invention is to provide a new and improvedjoint in a wound type core suitable for assembly with a preformedwinding or coil.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention, accordingly, comprises the several steps and the relationand order of one or more of such steps with respect to each of theothers, and the apparatus embodying the features of construction,properties, and the relation of elements which are exemplified in thefollowing detailed disclosure, and the scope of the application of whichwill be indicated in the claims.

atcnt "ice For a fuller understanding of the nature and objects of theinvention, reference should be had to the following detailed descriptiontaken in connection with the accompanying drawings, in which:

FIGURE 1 is a view in end elevation showing how the turns of a core arewound in accordance with this invention;

FIG. 2 is a view in end elevation of the core shown in FIG. 1 with theturns out to provide independent laminations;

FIG. 3 is a view in end elevation of the core showing how thelaminations are arranged in stepped relationship;

FIG. 4 is a fragmentary view showing the laminations separated intogroups with the ends disposed in stepped relationship;

FIG. 5 is a fragmentary view showing the joints of the outermost groupof lam-inations of a core displaced relative to the joints of the innergroups;

FIG. 6 is a fragmentary view showing a second embodiment of a core inwhich the joint of the outermost lamination of the core is displacedrelative to the joints of the outermost group of laminations;

FIG. 7 is a View partly in section and partly in side elevation of acore and coil assembly showing how the cores may be fitted through thewindow of a preformed winding or coil after a core constructed as shownin FIG. 5 has been shaped;

FIG. 8 is a fragmentary view showing a core and coil assembly completelyassembled after the last group of laminations of each core shown in FIG.7 has been fitted through the Window of a preformed winding;

FIG. 9 is a top view of a core and coil assembly, including coresconstructed in accordance with FIG. 6, with the outermost laminations ofeach core secured to the next adjacent lamina-tion;

FIG. 10 is a View in end elevation of a third embodirnent of a coresimilar to the core shown in FIG. 1 except that the outermost laminationis provided with an overlapping portion which remains after the turns ofthe core are cut; and

FIG. 11 is a top view of a core and coil assembly including a corehaving an outermost lamination with an overlapping portion constructedin accordance with FIG. 10.

Referring now to the drawings and FIG. 1 in particular, a Wound typecore is shown generally at 10 having a plurality of turns 12 of orientedmagnetic strip material wound on one another. The core 10 has apredetermined number of turns of magnetic strip material wound in aclosed loop which preferably has substantially a ring shape, but mayhave any other desired shape in a closed loop which need not becircular, as illustrated. The thickness and width of the magnetic stripand the number of turns are determined by the necessary capacity of thefinal core and the dimensions of the preformed winding with which thecore is to be assembled.

The core 10 shown in FIG. 1 may be wound by any of several, well-knownsuitable means. The core 19 may be annealed after it is wound insubstantially a ring shape as shown or alternatively, the turns of thecore may be retained in the ring shape or closed loop by any suitablemeans, such as precurving during the Winding of the core.

Referring to FIG. 2, the core 10 is next cut or severed along a line 22substantially at right angles to the turns 12 to provide independentlaminations 12, which are equal in number to the number of turns in thecore 19 before it is cut, in order that the core 1d may be fittedthrough the window of a preformed winding.

In order to prevent spreading by formation of burrs during cutting ofthe core 10, it has been found necessary to clamp the core 10 near theline 22 on each side by suitable means (not shown). If the core 12 hassubstantially a ring shape as illustrated, the out along the line 22would be along a diameter of the ring-shaped core 10, but the cut alongthe line 22 may be varied somewhat to meet a special purpose in aparticular core embodying this invention.

Referring to FIG. 3, after the core 10 is cut, the laminations 12 of thecore 1d are separated into groups by any suitable means such as thefixture or jig 60 having a plurality of curved grooves or recesses 62,63 and 66 in order to arrange the cut ends of the laminations 12 in adesired pattern. As illustrated, the laminations 12 of the core 10 areshown partially arranged into three groups 24, 34, and 44, each grouphaving a plurality of laminations disposed with the ends of'eachlamination offset or displaced from the cut ends of the adjacentlamination in a stepped relationship. Each lamination of the core 19forms a joint which is offset or staggered with respect to the joint ineach adjacent lamination. The out ends of each lamination lap the cutends of each adjacent lamination. The end portion of each laminationoverlaps the end portion of the next adjacent lamination to form a jointwhich may be described as a stepped-lap joint because of the manner inwhich the cut ends of the laminations are disposed. v

Referring to FIG. 4, after all of the laminations -12 of the core 10have been arranged in groups with the cut ends of the laminations 12 instepped relationship, the groups 24, 34, 44 and 54 of the laminations 12are then assembled to make a series of stepped-lap joints in a closedcore. The groups of the laminations 12 may be arranged in a recurringpattern as shown in FIG. 4. The number of laminations 12 in each groupneed not be the same and may be varied to suit particular designrequirements. Each of the groups 24, 34, 44 and 54, as illus trated,preferably consists of at least seven individual laminations. The butends of each of the laminations 12 are substantially aligned with oneanother forming a joint that is offset or staggered with respect to thejoint in-the adjacent lamination in the order of to times the thicknessof each lamination to form a stepped joint in each group whose length ispreferably substantial compared to the thickness of the core. Asillustrated in FIG; 4, the groups 24, 34, 44 and 54 are superimposed onone another forming an overall stepped joint that extends through asubstantial sector of the core. The cut ends of the laminations 12 mayabut one another as illustrated, but this is not essential to the coresince satisfactory results have been obtained the cut ends of eachlamination spaced from one another by a distance equal to the thicknessof one or two of the laminations 12. The ends of the laminations 12should overlap one another by a substantial amount, preferably by adistance equal to or in excess of six times the thickness .of one of thelaminations 12. g

It is to be noted that the ratio of the overlapping distance to thethickness of a lamination may be varied in a particular application toobtain a more balanced magnetic reluctance from the inside of the coreto the .outside of the core by making the ratio progressively largerfrom the innermost group to the outermost group of laminations. Thiswould compensate for the variation in the length of the laminations fromthe inside to the outside 12 have been assembled as shown in FIG. 4, atleast one of the outermost groups of laminations, such as the group '54,is displaced or shifted by a predetermined amount or distance relativeto the joints of the inner groups of the laminations 12 which includethe balance or rest of the groups 24, 34 and 44. As will be explainedhereinafter, the amount or distance that the group 54 is displaced willdepend on the desired location of the joints or the outermost group orgroups of laminations on the final shaped core. Several steps inobtaining the arrangement of the laminations 12 shown in FIG. 5, may becombined by substituting a special fixture or jig (not shown) for thefixture 60 shown in FIG. 3, the special fixture having the outermostgroup or groups separated by a disproportionate amount frorn'the othergroups in the special fixture (not shown) in order that at least thejoints of one of the outermost groups be displaced relative to thejoints of the inner groups as shown in FIG. 5. The latter method wouldallow at least the joints of one of the outermost groups to be displacedor shifted in one direction for a particular prior arrangement of thegroups relative to the joints in the balance of the groups.

Referring to FIG. 6, a second embodiment of a core embodying theteachings of this invention is illustrated in which the joint in theoutermost of the laminations 12 is displaced or shifted relative to thejoints of the displaced. group or groups shown in FIG. 5. In particular,the cut ends of the outermost of the laminations 12 shown at the line 32is shifted back to its original position before the outer group 54 isdisplaced. For reasons which will be explained hereinafter, the cut endsof the outermost of the laminations 12 will then be disposed or locatedon the same portion of the final shaped core as the inner groups 24, 34and 44 whose joints were not displaced.

After the groups of the laminations 12 have been as sembled as shown inFIG. 5, the core is next shaped to a predetermined shape suitable forassembly with a preformed winding (not shown). The core is usuallyshaped to a substantially rectangular shape as shown in FIG. 7. Afterthe core is shaped, it will be annealed to re: lieve stresses set up inthe core by the shaping step by any of several suitable means which areWell-known in the art. Afiter the core has been shaped and annealed, thecore is: disassembled to the extent necessary to fit the core throughthe window of a preformed winding or coil. Disassembly of the core isfacilitated by the fact that bonding of the laminations is not required.It has also been found that it is unnecessary to work the cut ends ofthelarninations to remove burrs since any burrs present would bedisposed in contact with an insulating layer provided on the magneticstrip material used to wind the core.

Referring to MG. 7, the manner in which two cores constructed inaccordance with this invention are fitted through the window of apreformed winding or coil 20 is illustrated. Each of the cores 5%includes a plurality of groups 24, 34, 44, 54, 64, 74, 34 and 94 oflaminations. All of the groups except the outermost group 94am shownalready fitted through the window of the preformed winding 20, the stepjoint in all of the groups except the outermost group 94 being disposedor located on the yoke of each of-the cores 5% The cut ends of thelaminations of the outermost group 94 which are shown generally atthelines 72- were displaced from the joints of the rest of the groups ofthe laminations in each of the coresSt) in a similar manner to thatshown inFiG.

5. By displacing thestep joint of the outermost group 94 relative to thestep joint in'the balance of the groups, the cut ends or'joints of thelaminations in the outermost group 94 are disposed or located, as shown,on a leg of each of the cores 50. i

. Referring to FIG. 8, the complete core and coil assembly including thecores 5d and the preformed winding 2% is illustrated after the outermostgroup 94 has been fitted in thewindow of the preformed winding 20. it isto be noted that an overall joint is obtained in which the step jointsof the groups of laminations are divided or distributed between the yokeand leg portions of each of the cores St). The slope of the cut ends ofthe laminations of the outermost groups 94 disposed on a leg of each ofthe cores 50 may be in either direction, the preferred slope being asshown in order that a flat plate or shim (not shown) may be used to fitthe cut ends of the outermost group 94 of displaced laminations into thewindow of the preformed winding 20. Any fiat plate or shim (not shown)used to fit the outermost group 94 into the window of the preformedwinding 20 would be removed after assembly of the cores 50 and thewinding 26. After the cores 5% and the preformed winding 20 have beencompletely assembled as shown in FIG. 8, any suitable means may beprovided, such as a band (not shown), around each of the cores 50 tomaintain the shape of each of the cores 50.

It has been found that deformation of the outer groups of laminations issubstantially eliminated in the fitting of these laminations through thewindow of a preformed winding 2.0 such as illustrated in FIGS. 7 and 8.This is because the stepped joint of the outermost group 94 of the cores5G is disposed on a leg of each core and may be fitted through thewindow of the preformed winding 20 without difficulty or bending andwithout the usual space between the cores such as required in aconventional core and coil assembly of this type. Thus, the space in thewindow of the preformed winding 20 is utilized to a maximum degree witha resulting economy in the amount of conductor required for thepreformed winding 20. Also the losses of a core constructed asillustrated in FIGS. 7 and 8 are reduced because of the absence ofdeformation of the outermost group or groups of laminations disposed onthe inner legs of the cores 50.

It is to be understood that although the core and coil assembly shown inFIGS. 7 and 8 are illustrated with only one outer group displaced so asto be located or disposed on the legs of the cores 50, a core embodyingthis invention could be constructed with two or more of the outermostgroups disposed on a leg of a core similar to the cores illustrated inFIGS. 7 and 8. It is also to be understood that the outer groups 94which are each disposed on an inner leg of the cores 5% could bedisposed on the outer legs of the cores 50 rather than on the inner legsas illustrated in FIGS. 7 and 8. In addition, a core embodying theteachings of this invention could be provided in which the outerdisplaced group or groups could be disposed on the yoke of the core andthe balance of the inner groups disposed on a leg or legs of the core byproperly arranging the joints of the laminations of the core before itis finally shaped. The arrangement shown in FIGS. 7 and 8 is preferred,however, for convenience in the making of core and coil assemblies asillustrated and allows easier inspection of the major portion of thejoint during assembly of the cores 5% and the winding 20.

Referring to FIG. 9, a core and coil assembly is illustrated including apreformed winding or coil 30 and the cores 42 which have beenconstructed in accordance with the arrangement shown in FIG. 6. In thisembodiment of the invention, the cut ends of the outermost lamination oneach of the cores 42 is disposed on the yoke of each of the cores afterthe cores are finally shaped as indicated generally along the line 32 oneach of the cores 42. Except for the outermost lamination of each of thecores 42, the making of the cores 42 would be similar to the stepsalready described for the cores 59 shown in FIGS. 7 and 8. In theembodiment shown in FIG. 9, however, the outermost lamination isdisposed with the cut ends of the outermost lamination on the yoke ofeach of the cores 42 so that the outermost lamination may be secured tothe next adjacent lamination thereby maintaining the shape of the cores42 after the cores and the preformed winding 35 are completelyassembled. In this instance, the outermost lamination of each of thecores 42 is secured to the next adjacent lamination by the spot welds162 which are disposed on each side of the cut ends of the outermostlamination of each of the cores 42. In this embodiment of the invention,therefore, it is not necessary to provide a separate means formaintaining the shape of the cores 42 after they have been fittedthrough the window of the preformed winding 3%. It is to be understoodthat means other than spot welds may be employed to secure the cut endsof the outermost lamination of the cores 42, such as a suitable tape.

Referring to FIGS. 10 and ll, a third embodiment of a core whichincorporates the teachings of this invention is illustrated. The makingof the cores 8% shown in FIG. 10 differs from the making of the cores 50shown in FIGS. 7 and '8 in that, prior to the cutting of the turns 82 ofeach of the cores St), the outermost turn is pulled back from the restof the turns 82. as illustrated in FIG. 10. The core is then out along adiameter at substantially right angles to the turnsv 82 leaving theoutermost lamination of the core 80 with a portion that overlaps the cutends of the rest of the laminations 32 of the core 8%. The overlappingportion of the outermost lamination of the core 80 is indicated at MP4in FIG. 11. The additional steps in making the core 8% are the same aspreviously discussed for the cores 59 shown in FIGS. 7 and 8.

Referring to FIG. 11, a core and coil assembly including a preformedwinding 49 and the cores 8% constructed as indicated in FIG. 10 isillustrated. The overlapping portion 1M of the outermost lamination ofeach of the cores 8G is secured to the next adjacent lamination by thespot welds 106. The latter arrangement also eliminates the need forseparate means such as bands for maintain ing the shape of the cores 319after they have been fitted through the window of the preformed winding46. The embodiment shown in FIGS. 10 and 11 requires less spot welds tosecure the outermost lamination to the next adjacent lamination than theembodiment shown in FIGS. 6 and 9. It is to be understood that theoverlapping portion 1% which is shown as disposed on the yoke of thecore 89 might also be conveniently located on the legs of the cores fit)in a particular design.

It will be readily appreciated that a magnetic core embodying theteachings of this invention may be constructed by means other thanwinding magnetic material. For example, magnetic material which has beencut or sheared into punchings of various lengths which are then shapedas required may be assembled into a core as shown in FIG. 8.

It is to be understood that the arrangement of laminations shown in FIG.6 may be obtained directly from the arrangement of laminations shown in'FIG. 4 by displacing all of the la-minations 12 in the outermost group54 except for the outermost lamination of the group 54 whose cut endsare shown at 32 in FIG. 6. It is $50 to be understood that a coreembodying the teachings of this invention could be constructed havingonly one group of laminations arranged to form a series of step-lappedjoints. In this case the joints of at least a portion of the outermostlaminations would be shifted or displaced relative to the joints of theinner laminations so that after the core was finally shaped the jointsin the laminations would be divided or distributed between the yoke andlegs of the core. In addition, a core embodying the teachings of thisinvention preferably includes only one overall cut of the turns, but thecore may include additional cuts with a corresponding increase in thelosses. One out per core would normally be used for a shell form typetransformer designed as shown in FIG. 9 and two cuts would normally beused with a core form transformer (not shown) which has one core and twowindings.

The apparatus embodying the teachings of this invention has severaladvantages, for example, a wound type core embodying the teachings ofthis invention, with groups of laminations distributed between the yokeand legs of the core, eliminates the space between two cores ,fittedinto the window of a preformed winding thereby improving the spacefactor and reducingthe amount of conductor required for the preformedwinding. In addition, the outer laminations can be more easily fittedinto the window of a preformed winding substantially eliminating thedeformation of the outer laminations, and

A core embodying the teachings of the invention shown in FIGS. 9 and 11would have an additional advantage of not requiring a separate means,such as a band, for maintaining the shape of the core after the core hasbeen fitted into the Window of a preformed winding.

A core constructed in accordance with this invention permits convenientclamping during manufacture.

The weight of the coil also assists in maintaining the joint afterassembly. Easier inspection of most of the joint is also possible duringassembly. The core combines the advantages of allowing convenientassembly of most of the groups of laminations on the'yoke portion Whilethere is ample room and convenient assembly of the outermost laminationson the leg portion when there is less room available to thereby preventdeformation of the outermost laminations.

It has also been found that a core having only one cut, constructed inaccordance with the teachings of this invention is an extremely low losscore with a very low exciting current and with a very, low sound level.

Since numerous changes in carrying out the above described process andcertain modifications in the apparat-us which embody the invention maybe made without departing from the spirit thereof, it is intended thatall the matter contained in the foregoing description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

I claim as my invention:

1. The method of making a magnetic core for use in a preformed coil,comprising the steps of, winding a predetermined number of turns oforiented magnetic strip material to form a core loop, cutting the'coreloop along a line at substantially right angles to the turns to provideindependent laminations, so arranging the laminations in a plurality ofgroups superimposed on each other in a recurring pattern that each grouphas a plurality of lamin-ations disposed with the ends of eachlamination displaced from the ends of each adjacent lamination in astepped relation, assembling the groups of laminations with stepped endsto make stepped-lap joints in a closed core, displacing the joints ofthe outer group a predetermined distance relative to the joints of theinner groups, so shaping the core to a predetermined shape having a yokeand legs that the joints of said groups are divided with the joints ofthe inner groups on the yoke and with the joints of the outer'group onthe inner leg of said core when the core is assembled in the window of acoil, and annealing the shaped core to relieve stresses.

2. The method of making a magnetic core for use in a preformed coilcomprising the steps of, winding a plurality of turns of orientedmagnetic strip to form a closed loop, cutting the core along a linesubstantially at right angles to the turns to provide independentlaminations, displacing the cut in each turn with respect to the cut ineach adjacent turn, so arranging the individual turns with the out endsof each turn opposite each other and with the cut in each turnoverlapping the cut in each adjacent turn that the cuts provide astepped joint in the .core, displacing the cuts in the outer turnsrelative to the cuts in the inner turns, so shaping the core to a'desired shape having a yoke and legs that the displaced 'cuts in theouter turns and the cuts in the inner turns are divided with the jointsof the innerturns on the yoke and with the joints of the outer turns onthe inner leg of said core when the core is assembled in the window of acoil, with most of said joints being in said yoke, and annealing theshaped core to relieve stresses.

thus substantially eliminating the increase in core losses I whichresult from deformation of the outer laminations,

3. The method of making. a magnetic core comprising the steps of,winding a plurality of turns of oriented magnetic strip to form a closedloop, cutting the core along a line substantially at rightangl'es to theturns to provide independent laminations, displacing the cut in eachturnwith respect to the cut in each adjacent turn, so arranging theindividual turns with the cut ends of each turn opposite each other andwith the cut in each turn overlapping the cut in each adjacent turn thatthe cuts provide a stepped joint in the core, displacing the cuts in theouter turns relative to the cuts in the inner turns, said outer turnsbeing less in number than said inner turns, so shaping the core to adesired shape having a yoke and legs that the displaced cuts in theouter turns are on the inner leg of said core when the core is assembledin the window of a coil and the cuts in the inner turns are on the yoke,and annealing the shaped core to relieve stresses.

4. The method of making a magnetic core comprising the steps of windinga plurality of turns of oriented magnetic strip material to form a coreloop, displacing the outermost turn to leave a predetermined spacebetween said outermost turn and the balance of said turns, cutting thecore loop along a line substantially at right angles to the turns toprovide independent laminations, pulling the outermost lamination tightto close the space between said outermost lamination and the rest ofsaid. laminations with a portion of the outermost lamination overlappingthe cut ends or the rest of said laminations, so arranging thelaminations in a plurality of groups that each group has a plurality oflaminations disposed with the cut ends of each lamination displaced fromthe cut ends of the adjacent lamination in a stepped relationship,assembling the groups of laminations with stepped ends to makestepped-lap joints with the ends of the groups in substantial alignment,displacing the joints of the outer group a predetermined distancerelative to the joints of the rest of said groups, so shaping the coreto a predetermined shape having a yoke and legsthat the joints of saidinner groups are on the yoke and the joints of the outer group are onthe inner leg of said core when the core is assembled in the window of acoil, annealing said core to relieve stresses, and securing theoverlapping portion of said outermost lamination to the adjacentlamination.

5. The method of making a core and coil assembly for inductiveapparatus, comprising the steps of, winding a coil to a predeterminedshape having a window for receiving a core, winding a plurality of turnsof oriented magnetic strip material to form a substantially ring-shapedcore, cutting the ring-shaped core along a diameter of the ring-shapedcore to provide independent laminations equal in number to the number ofturns in the core, so

arranging the laminations into a plurality of groups that each group hasa plurality of laminations disposed with the ends of each laminationdisplaced tfrorn the ends of the adjacent lamination in a steppedrelationship, assembling the groups of laminations with stepped ends tomake stepped-lap joints in a closed core, displacing the joints of theouter group relative to the joints of the balance of the groups, soshaping the core to a predetermined shape having a yoke and legs thatthe joints of the displaced group are disposed on the inner leg of saidcore when the core is assembled in the window of a coil and the jointsof the rest of said'groups are disposed on the yoke of said core,disassembling the shaped core in groups of laminations, and reassemblingsaid groups of .laminations in the window of said coil with the ends ofeach lamination in substantial alignment with each other.

6. The method of making a core and coil assembly for inductive apparatushaving two adjacent cores tor one coil, comprising the steps of, winding'a coil to a predeter-mined shape having a window for'rec'eivintg thecores, making each core by winding a plurality of turns of orientedmagnetic strip material to form a substantially ringshaped core, cuttingthe ring-shaped core along a diameter of the ring-shaped core to provideindependent laminations equal in number to the number of turns in thecore, so arranging the laminations into a plurality of groups that eachgroup has a plurality of laminations disposed with the ends of eachlamination displaced from the ends of the adjacent lamination in astepped relationship, assembling the groups of laminations With steppedends to make stepped-lap joints in a closed core, displacing the jointsof the outer group relative to the joints of the balance of the groups,so shaping the core to a predetermined shape having a yoke and legs thatthe joints of the outer group are disposed on the inner leg otf saidcore and the joints of the rest of said groups are disposed on the yokeof said core, annealing the shaped core to relieve stresses,disassembling the shaped cores in groups of laminations, andreassembling said groups it? of laminations for each core in the windowof said coil with the ends of each lamination in substantial alignmentWith each other and the legs of the cores having the joints of thedisplaced groups thereon adjacent each other.

References Cited in the file of this patent UNITED STATES PATENTS1,935,426 Acly Nov. 14, 1933 2,288,855 Steinmayer et a1. July 7, 19422,484,214 Ford et al. Oct. 11, 1949 2,931,993 Dornbush Apr. 5, 19602,960,756 Treanor Nov. 22, 1960 2,972,804 Ellis Feb. 28, 1961 FOREIGNPATENTS 624,137 Great Britain May 27, 1949

2. THE METHOD OF MAKING A MAGNETIC CORE FOR USE IN A PREFORMED COILCOMPRISING THE STEPS OF, WINDING A PLURALITY OF TURNS OF ORIENTEDMAGNETIC STRIP TO FORM A CLOSED LOOP, CUTTING THE CORE ALONG A LINESUBSTANTIALLY AT RIGHT ANGLES TO THE TURNS TO PROVIDE INDEPENDENTLAMINATIONS DISPLACING THE CUT IN EACH TURN WITH RESPECT TO THE CUT INEACH ADJACENT TURN, SO ARRANGING THE INDIVIDUAL TURNS WITH THE CUT ENDSOF EACH TURN OPPOSITE EACH OTHER AND WITH THE CUT IN EACH TURNOVERLAPPING THE CUT IN EACH ADJACENT TURN THAT THE CUTS PROVIDE ASTEPPED JOINT IN THE CORE, DISPLACING THE CUTS IN THE OUTER TURNSRELATIVE TO THE CUTS IN THE INNER TURNS, SO SHAPING THE CORE TO ADESIRED SHAPE HAVING A YOKE AND LEGS THAT THE DISPLACED CUTS IN THEOUTER TURNS AND THE CUTS IN THE INNER TURNS ARE DIVIDED WITH THE JOINTSOF THE INNER TURNS ON THE YOKE AND WITH THE JOINTS OF THE OUTER TURNS ONTHE INNER LEG OF SAID CORE WHEN THE CORES IS ASSEMBLED IN THE WINDOW OFA COIL, WITH MOST OF SAID JOINTS BEING IN SAID YOKE, AND ANNEALING THESHAPED CORE TO RELIEVE STRESSES.